The object of the present invention is a joint for door frames and other similar frame structures or sections. These include, among others, window casements and frames, picture frames, etc. The invention is preferably applied to jointing frames or the like, made of wood, but it is also fit for jointing parts or sections made of other materials, for instance plastic.
Door frames, casements, and other similar structures or sections are nowadays generally manufactured in ready-made elements by sash and door factories or carpenters' workshops, and then mounted in their respective positions at buildings sites. The highly developed standardisation of doors and windows had made it possible to produce them in large series. The frames and casements produced in series are manufactured using traditional carpenter's joints, the so-called claw joints; these require the use of special routers and are comparatively laborious to produce. Thus it is usually possible to manufacture the joints only industrially.
On the other hand, the transportation of ready-made casements and frames is uneconomical, since they take up a relatively large space.
Corner joints for frames with junction plates or bracings of metal are previously known. U.S. Pat. No. 1,334,553 and German Pat. No. 816,749 can be referred to as examples. These introduce joints, in which junction plates of metal are placed in a groove in the frame. The junction plates have been attached to the frames by nailing. In the U.S. patent they are nailed on either the inner or the outer surface of the frame, and in the German patent on the lateral surface of the frame.
U.S. Pat. No. 1,392,070, gives a junction of plate of metal, which is attached to the frame with die-cut teeth. A similar solution is also given in Swedish patent application No. 1773/71 A drawback of the solutions presented above is the awkwardness and slowness of their use. This is due to the difficulty of using nails or the complicated pressure devices needed. Moreover, nails are not desirable on the surface of the frame.
U.S. Pat. No. 1,959,360 discloses a nail for a corner joint. The nail has a flat body with an arrowheaded tongue in one end and a V-shaped groove in the opposite end. Along the sides of the flat body, the nail is provided with flanges which diverge from the arrowheaded end to the grooved end. The sections of wood to be jointed are mitered and grooves are cut on the respective positions within the mitered edges to serve as guides for the nail. When the nail is pressed, the V-shaped end moves ahead, i.e. from the outer corner into the groove of the corner joint, and the flanges bite into the walls of the groove and draw the sections tightly together. The length of the nail is prechosen so that it extends through the whole corner joint.
Two drawbacks can be mentioned in connection with the above-described nail. The flanges of the nail may split the wood along the groove of the sections of the frame especially if these sections are made of hard wood. The nail should be as long as the mitered edges of the sections. Hence, the nail which can be used depends on the breadth of the sections of the frame.
In U.S. Pat. No. 1,779,729 is described a nail with a corrugated body plate. The nail is used for securing together strips of wood which form a block in making parquetry. The strips are jointed together along their longitudinal edges by tongue and groove portions. Furthermore, the strips are provided with end grooves for jointing crosswise an adjacent block with them. The parallel strips are secured together with the nails at the opposite ends of the strips. Each nail is driven into the wood along the grain in the end groove until it is flush with the bottom of the groove.
The purpose of the corrugation in the body plate according to U.S. Pat. No. 1,779,729 is to make the nail rigid and to prevent it from splitting the wood when the whole nail is driven deeply inside the strips of wood. Nevertheless, the nail may still split the wood, especially if the strips are made of hard wood.
U.S. Pat. No. 1,663,580 describes a fastener for fastening together two pieces of wood, for instance, in the manufacture of boxes. The fastener comprises a round corrugated metal plate adapted to be inserted into semi-circular grooves cut into the joining faces of the pieces of wood to be fastened together. Tongues are provided which project from the plane of said metal plate and are adapted to bite into the wood upon a turning of said metal plate in the groove.
The turning of the metal plate according to U.S. Pat. No. 1,663,580 requires a special key for insertion into a hole in the middle of the metal plate and through a hole which has to be provided in the joining faces of the two pieces of wood. The metal plate must not fit very closely within the grooves so as not to render difficult its turning. However, consequently, the metal plate can give only limited resistance against forces exerted onto the joint. Furthermore, the cutting of the semi-circular grooves into the joining faces is laborious.